Recently, it has been suggested that between-group contest competition and male resource defense have been underestimated in nonhuman primates. In many species, food resources within the group’s core area may depend on the resource holding potential of resident males. Among Argentine tufted capuchin monkeys (Cebus apella nigritus), dominant and subordinate males cooperate to defend immediate access to high-quality food resources. Here I investigate consequences of this male-male cooperation for intergroup dominance relationships and home range quality. I recorded ranging behavior for four habituated groups in Iguazú National Park for 16 months to identify home ranges and core areas. I measured the availability of food species within botanical plots placed in each group’s core area, using a stratified random sampling. I recorded the location and outcome of intergroup encounters, and performed generalized-linear mixed models toassess the relative importance of male group size and encounter location on the outcome. Relative male group size was the most important factor in determining the winner of encounters, outweighing the competitive advantage of ownership. Average core area size was positively correlated with male group size, but neither the density of food species nor the total availability of food resources within the core area was influenced by the group’s competitive ability. Dominant groups are better able to defend their core area, however, and adjusting for the degree of home range overlap revealed that dominant groups may have higher per capita access to food. These results suggest that male-male cooperation could ultimately increase female reproductive success.

This study was funded by the Leakey Foundation, National Geographic Society, the National Science Foundation (DDIG BCS-0752683; BCS-0515007 to CH Janson), the Wenner-Gren Foundation (7929).